Electrical Fundamentals
Source Internal Resistance Calculator
Source Internal Resistance is a worksheet for comparing one electrical condition at a time, with the result tied to its inputs.
Run a Source Internal Resistance check
Use measured values for Source Internal Resistance when available and rated values only when they describe the same condition.
Where Source Internal Resistance fits
Use the page when internal resistance needs to be checked without rebuilding the equation by hand. The surrounding notes define how far the number should be carried.
Operating notes for Source Internal Resistance
Source Internal Resistance is simple only after the material, temperature, and measurement condition are known.
Sample Source Internal Resistance run
Using the sample values, Open-circuit voltage = 12.6 V; Loaded voltage = 11.8 V; Load current = 20 A, the primary result is 0.0400 Ω.
This Source Internal Resistance one-input test is a scale check, showing direction and sensitivity without turning the changed case into a recommendation.
Math notes for internal resistance
Read the Source Internal Resistance equation from the units on this page. A familiar symbol can shift meaning between DC, AC, energy, component, or billing work.
A clean Source Internal Resistance result confirms the arithmetic for internal resistance; it does not prove the equipment rating or source data is the right one.
Only the entries shown on Source Internal Resistance feed internal resistance. If another correction factor matters, keep it in the notes or make a separate run.
| Displayed value | Default case |
|---|---|
| Internal resistance | 0.0400 Ω |
| Internal power loss | 16.00 W |
Keeping load current tied to the case
Each Source Internal Resistance entry should describe the same circuit, device, billing period, or test condition. Mixed sources can make a plausible but wrong result.
Open-circuit voltage is shown as 12.6 V. Enter open-circuit voltage in V.
Loaded voltage is shown as 11.8 V. Enter loaded voltage in V.
Load current is shown as 20 A. Enter load current in A.
Reading internal resistance
The result card gives a comparison point for Source Internal Resistance. Equipment ratings, safety margins, and manufacturer limits still need their own check.
Use a consistent electrical model before comparing the Source Internal Resistance result with current, voltage, resistance, charge, or energy notes.
Boundaries for internal resistance
The source must be measured at a stable temperature and state of charge.
- Material tolerance
- Measurement resolution
- Transient behavior
A separate Battery Internal Resistance run is cleaner when that result becomes the real design question.
Help with internal resistance
What should be recorded with the answer?
Save the Source Internal Resistance inputs, unit basis, operating case, and result note so internal resistance can be reproduced later.
Which value should be rounded first?
Keep loaded voltage at source precision during Source Internal Resistance; round internal resistance only where presentation or purchasing requires it.
When should this be run again?
Run a new Source Internal Resistance case when the source condition changes, such as voltage, load, rate schedule, temperature, component, connection, or period.